Modern laptop computers are battery powered, and weigh less than perhaps 6 pounds (13.2 Kg), and are expected to operate for several hours before the battery requires recharging or replacement. Such computers include a high speed central processing unit ("CPU") and a liquid crystal display ("LCD"). The design of such computers involves conflicting considerations directed to cooling the CPU and to heating the LCD, while minimizing battery drain and weight.
On one hand, because the CPU is very compact and operates at a high clock rate that may exceed 50 MHz, the CPU dissipates several watts of power as heat (8 W for a "'586" or "Pentium" CPU). The surface of a '586 CPU may reach 95.degree. C., despite the use of a heat sink and/or a cooling fan. A heat sink adds weight and adds perhaps $8 to the manufacturing cost of a laptop. A fan adds even more weight, perhaps $12 in cost, and undesirably drains perhaps 2 W power from the battery, shortening battery operating time.
In an attempt to decrease weight and to eliminate fan power consumption, CPUs are cooled using heat pipes through which fluorine or water is passively circulated. Although such techniques can cool a CPU, a leak in the cooling system can go undetected. The result is that the uncooled CPU (typically a $400 component) can overheat and self-destruct within a minute or so.
On the other hand, although it is necessary to cool the CPU, it may also be necessary to heat the LCD to prevent it from becoming sluggish or inoperable at temperatures below about -9.degree. C. In fact, laptop computers designed to military specification include a mesh-like wire heating element disposed behind the LCD display. This heating element permits normal LCD operation at such low temperatures but consumes about 3-5 W of power from the laptop battery. Unfortunately, the power required to heat the LCD shortens the battery operating time.
Thus, there is a need for an inexpensive, light weight system for cooling a CPU in a laptop computer, which system permits instant detection of a cooling system failure. Further, there is a need for a system for heating a LCD in a laptop computer without using power from the laptop battery.
The present invention discloses a system that fulfills both of these needs.